[sox and martin]

I put a TB 140 in my Gpx. I also used the Crower g2 cam. I used good pump fuel riding it today. The thing quit during the second moto.The crown was cracked aslost exactly to the shape of the ring land. Has this happened to anyone else? Do I need to be using race gas? I also damaged the exhaust valve. WOuld it be worth it to rebuild and got to a big valve head? One lobe on the cam was a bit scored too, is this an issue with these cams?

 

[FastMC]

I ran that same exact setup for many hours with no issues. Ran fine on high test pump gas. Were you getting good oil flow to the head. Sounds as though you cooked it and maybe starved the top end of oil.

 

[sox and martin]

Nope, there is no scoring whatsoever.The crown cracked due to detonation as far as I can tell. The oiling wasn't an issue on my 125. I heard it ping a couple of times. I guess it was worse than I thought.

 

[melloyello]

What octane were you using? Also, was it jetted correctly? If it was too lean then it would have gotten pretty hot. The hotter the engine gets the more apt it is to detonate especially if jetting is off or high enough octane fuel is not used.

 

[Kurlon]

If a cam lobe scored, the top end wasn't getting enough oil.

 

[GMRaceworx]

Sounds like you were running lean and got the temps way up then everything started to disintegrate.

 

[firepower354]

Was the spring in coil bind? That can smoke a cam.

 

[sox and martin]

Was the spring in coil bind? That can smoke a cam.

I'll check that thanks.

 

[melloyello]

Did you use silicone or some sort of gasket maker anywhere?

 

[StupidSheet]

Did you use silicone or some sort of gasket maker anywhere?

What would this cause? Not trying to be an ass, just curious.

 

[melloyello]

Well, if you use too much gasket maker on a base gasket or in place of a base gasket then you can clog up the oil passage leading to the top end.

 

[sox and martin]

Well, if you use too much gasket maker on a base gasket or in place of a base gasket then you can clog up the oil passage leading to the top end.

No signs of oil starvation whatsoever.

 

[melloyello]

Well, all I can say is it sounds like you ran it lean as all. That would cause the engine to get really hot and detonate. And if the cam lobe was scored then that could be a sign of a lack of oil but even if it isn't it stills sounds like you ran it lean. That's really all I can tell you. You can ask for second opinions but I am pretty sure that is what has happened.

Many and I mean many people have ran the 140 and 146 kits w/ no problems. The main thing you have to do w/ any big bore kits, cams, exhausts, and carbs is you have to rejet when something is done. And you can't guess at it. It can't be done in just a few minutes either. It takes time to do it correctly. Always run it rich when you first break it in. What carb were you running and what jets were in it and what's your elevation or where are you located?

 

[T Bolt USA]

hows the plug look ??



the tb kit is kinda high comp and race gas may be needed



the bvh will lower the comp and give better flow



we do also have a 1mm base gasket



and if its really a 140 i have a few pistons i can discount



let me know what you need

 

[sox and martin]

The plug is tan, not grey or white. The score in the cam may have been on initial startup or perhaps some piston debris got through there. The piston did break apart a bit. I asked about jetting it when I purchased the kit and was told it was rich to start with so I would be fine. Stock pitster carb. We are at 700 ft the temp was around 80, high humidity.. hard packed track. Is the Crower g2 a bit much for this application? My buddy has the same setup with a TB cam.. his bike rips. Could I punch it out ang go to a 146 now that I damaged it? What is req'd piston to cylinder clearance? Thanks to all for your input.

 

[dougtrip]

way to close on compression. you are running the stock gpx head you need to run race gas to be safe.

 

[sox and martin]

way to close on compression. you are running the stock gpx head you need to run race gas to be safe.

I am running the stock head. I compared it to another Lifan head. The intake tract on mine is twice the diameter??? I understand the compression ratio could be in the 12:1 range. I don't know what the timing is but race gas is almost certainly req'd or at least mixed with pump gas. That's my thinking anyway.

 

[T Bolt USA]

the tb 411 is a copy of the g2 so thats nothing



you can over bore to 57mm